Art of fractionation



RECEIVING Mae-Mm mun I I I W. M. STRATFORD vART 0F FRACTIONATION Filed Aug. 2, 1929 TOWER Sept. 19, 1933.

coou/ve CO/L mama/arm STILL VAPOR LINE HMT/AG COIL Patented Sept. 19, 1933 I I were srArss PATENT. "ome a ABT or FRACTIONATION William M. Stratford, New York, N. Y., assignor to The Texas Company, New York, 'N. Y., a corporation, of Delaware Application August 2, 1929. Serial No. 383,093

Claims. (01. 196139) tionated. Thus the invention has in view a process in which the fluid to be fractionated is introduced into thetower at a mid point therein with cooling applied at the upper end of the tower and heating applied at the lower end of the tower to thereby obtain the desired progressive temperature differential between the top and bottom of the tower to produce the desired fractionation while vapors are withdrawn from the tower at a point between that of the entry of the fluid to be fractionated and the bottom of the tower.

One of the objects of the invention is to form an intermediate fraction which contains constituents having a boiling range between that of the overhead vapor fraction and the bottoms or reflux condensate 4 Various objects and advantages of the invention appear in the following detailed description thereof in which reference is had to the accompanying drawing which is a diagrammatic sectional elevation of an apparatus constructed in accordance with the invention and constituting an embodiment thereof.

In the apparatus thus illustrated .a fractionating tower 10 is shown arranged to be sup' plied with vapors to be fractionated by a vapor line 11 which extends from a still or vaporizing chamber 12 to an intermediate point of the tower. A vapor line 13 is provided for removing the overhead vapor fraction to a condenser coil 14 and receiving drum 15, and a line 16. is provided for withdrawing the bottomsv or reflux condensate. a plurality of bubble trays 17 but if desired other suitable fractionating elements may be employed. A coil 18 is shown in the upper end of the tower for supplying cooling. ,It may be pointed out that any suitable cooling means may be employed in lieu of this coil, such as a refluxcondenser for the tower or the introduction of a cooling medium directly into contact with the fluid in the tower, such for exampleas maybe accomplished by directing a portion of the distillate from the receiver 15 back to the top of "the tower. At the bottom of the tower is shown a heating coil 19 which may, for example, be a 14 .and'coll'ected as a gasoline distillate The tower is shown equipped with 400 end point gasoline fraction an intermediate steam coil. If desired, instead of using a closed steam coil, steam or other heatingmediumfor carrier gas may be discharged into the bottom, of the tower. v I

A plurality of valved pipes 20 are shown communicating with the vapor' spaces between cer- Q0 tain of the trays 1'7 at pointsbelow-the point of entry of the vapors through thelinewl l. ,The lines 20xcommunicate with a commonline '21 which extends to a condenser coil 22, andreceiving drum '23. .In practicing' 'the inventionja single line 20 or a plurality of these'lines may" be used. The vapor fractions withdrawn may be separately condensed and collected as separate condensates or the several'vapor 'streams may be combined and collected as a single condensate 7 as in the apparatus shownin thedrawing. In order to more fully explain the 'inventiona, specific example thereof will begiven in which it" is desiredto make three distillates such as gasoe line, kerosene, and gas oil. The hydrocarbon oil 'or petroleum from which thesefractions' are to be obtained may be subjected to vaporization in any suitable distilling apparatus. Thus for example crude petroleum 'or' other. oil containing the desiredproductsfmay be passed through a tubular heater heated to temperatures of the order of'700 or 800. F., for example, and the heated products passed intoa still, such as' the still l2.- Vaporous products discharged from the. still may, for examplaconsistof gasoline, kero- 5 sene, and gas oil. and are passed therefrom throughthe vapor line 11 into the tower 10 at an intermediate point thereof- Heating is applied tothe bottom of the tower, as'by means of the coil19, and. cooling is applied to the upper endof the tower, as bymeans of the coil 18, so that a vapor fractionhaving, for example, an end point of F. may be taken off through the vapor line 13, condensed in the condenser in the receiver 15." v i In this example of the invention it is assumed thatit is desired to produce in addition to: the' or kerosene'fraction and aheavier or gas oil fraction and that it is desired that these three a fractions shall contain constituents the boiling points of which will notmaterially f overlap. It may be pointed out that such an intermediate fraction could not be made byldrawing off liquid from anyof the trays above the point of entry of the vaporiline 11 because the liquid on'a'ny of these trays will necessarily contain constituents boiling within the desiredgasoline range, the

proportion increasing upwardly from tray to tray and amounting to approximately 100 per cent on the top tray. Itwill also be seen that this fraction could not'be made by drawing off liquid from any of the trays below the point of entry of the vapor line 11 because this liquid will contain portions of the gas oil fraction which it is desired to draw off from the bottom of the tower,

this proportion increasing downwardly from tray to tray. Furthermore it will be seen that the desired intermediate fraction could not bemade by drawing off vapors from any point above that 1 of the entry of the vapor line" 11, since these vapors will necessarily contaiirgasoline constit-' from constituents boiling within the range of' the desired bottoms ,or gas oil-cut; is withdrawn from the tower as" a separate out. Thus this keros'enejor intermediate fraction may have, for

example,v an intial distilling point of 400 F. and

. an end point of 500 F. while the gas oil fraction collected at the. bottom' of the towerand withdrawnthrough the line 16 may have an initial boiling point of 5 00f F.

It is to be understood that the invention is applicable to the production of distillates or condensates other than those mentioned, herein, the references 'tothe specifically named products being for the purpose of giving a concrete'example of the invention. f j

Although the fractionating tower shown in the drawingis of the bubble tower type it is to be understood that other types of fractionating towers may be employed, the packing or contact T material being arranged'in sections and the vapors which constitute the intermediate fraction being drawn off from vapor spaces between sections. It will thus be seen that in practicing the invention the fluid to be fractionatedv may be introduced at a given pointina fractionatingapparatus and that by the application of cooling atone point and heating at another point a progressive temperature diiferential may be established through the apparatus so as to take oif a final vapor fraction of" desired boiling point and'a final reflux condensate of desired boiling point,'and by the withdrawal of a vapor fraction from a section of theapparatus which is at a higher temperature than that of the section to which the fluids to be fractionated are; admitted it is thus possible to produce an intermediate cut containing no components having boiling .points within the range of the final vapor frac tion and also, if desired, substantially free of components having boiling points of those' con- 'tained injthe ultimate reflux condensate made in the apparatus, a i i Inpracticing' the. invention it is generally'pref- -,erable to limit the quantity of vapor withdrawn through any of the lines 20. This maybe-accomplished bymanually crackingj the valves one or'rnore of the lines 20 through which it s desired to withdraw vapors, or these valves may be automatically controlled by thermostatic the tower and below that of the entry of the means operating in response to temperature conditions in the tower 1G. The invention has a special field of usefulness in connection with the cracking and distillation of hydrocarbon'oils under pressure. Thus, for example, in cracking systems wherein the vapors from the pressure still are subjected to fractionation in a pressure fractionating tower for the purpose of taking off an overhead gasoline distilate and bottoms or reflux condensate suitable for return to the cracking zone dimculty has been experienced due to the accumulation of intermediate constituents in the tower, which under the pressures employed will at the temperatures used at the top of the tower be in liquid-form so that they will not pass out with I the'vapors from the top of the tower and atthe temperatures employed in the bottom of the tower will be in'vapor form so that they willnot be removed with the reflux condensate withdrawn from the bottomof the'tower, the result being that these intermediate constituents tend to accumulate in the intermediate portions of the tower and thus reduce the capacity of the tower. In accordance with my invention the vapors from the pressurerstill are admitted to an intermediate point of the tower and'an in termediate cut is made by drawing 01f vapors at r a selected point or points above the bottom of 65 vapors, in this way removing certain-intermediate constituentsfrom the tower and thereby increasing the capacity of the tower. Y

Although the preferred embodiment of the invention has been set forth in connection with 110 apparatushaving a particular construction and arrangement of parts and mode of operation, it is obvious that various changes and momm tions may be made therein, while securing to a greater or less eXtentsome-or all of the'benefits of the invention, without departing from the spirit and scope thereof. Therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim: I v

1'. In the fractionationof hydrocarbon oils, the process that comprises introducing hydrocarbon vapors to be fractionated into an intermediatepoint of a fractionating tower, applying heat to the lower part of the tower and apply ing cooling to the upper part of the tower to thus establish and maintain a stream of upwardly risingvapor from'the bottom'of the tower to the top thereof and a' stream of downflowing' liquid from the top of the tower to the bottom thereof, with a graduation of temperature through the tower so that the upwardly rising vapor is subjected 'to progressively lower temperatures and the downfiowing liquid is subjected to progress sively higher temperatures tothus subject the upwardly rising vapors to repeatedbondensations and the downflowing liquid to repeated vaporizations to thereby efiect fractionation in'the tower, and withdrawing vapors'from an intermediate point in theltower below that of the entry of the yaporsto be fractionated.

2. In the fractionation of hydrocarbon oils,

the process that comprises introducing hydro- Cir.

temperatures and the downflowing liquid is subjected to. progressively'higher temperatures to -thus subject the upwardly rising vapors to repeated condensations'and the downfiowing' liquid to repeated vaporizations to thereby effect fractionation in the tower, taking off anpverhead vapor fraction, withdrawing refiux' condensate from the lower part of the tower, and withdrawing an intermediate cut'by taking off vapors from a point below that of the entry of the vapors to be fractionated wherein the vapors are substantially free of constituents of the boiling point of those contained in the overhead vapor fraction.

3. In the fractionation of hydrocarbon oils, the process that comprises introducing hydrocarbon vapors to be fractionated into an intermediate point of a fractionating tower, applying heat to the lower part of the tower, whereby said portion is maintained at a temperature higher than that of the point of entry of the vapors, and applying cooling to the upper part of the tower to thus establish and maintain a stream of upwardly rising vapor from the bottom of the tower to the top thereof and a stream of downflowing liquid from the top of the tower to the bottom thereof, with a graduation of temperature through the tower so that the upwardly rising vapor-is subjected to progressively lower temperatures and the downflowing liquid is subjected to progressively higher temperatures to thus subject the upwardly rising vapors to repeated condensations and the downflowing liquid to repeated vaporizations to thereby effect fractionation in the tower, taking off an overhead vapor fraction and a reflux condensate fraction from the tower and withdrawing an intermediate cut by taking off vapors from a section of the tower that is at higher temperature than that of the point of entry of the vapors to be fractionated.

4:. The method of fractionating hydrocarbon oil vapors which comprises introducing hydrocarbon oil vapors into a fraotionating tower at an intermediate point thereof, cooling the upper portion of the tower to effect fractionation of vapors therewithin, subjecting resulting condon sate to vaporization at a point within said tower below the point at which said vapors are introduced, separately withdrawing from the tower an overhead vapor fraction and unvaporized portions of said condensate, and separately withdrawing an intermediate cut by taking off vapors from a section of the tower intermediate the point at which vapors are introduced and no point at which said condensate is subjected to vaporization.

5. The method of fractionatlng hydrocarbon oil vapors which comprises introducing hydro carbon oil vapors into a fractionating tower at an intermediate point thereof, cooling the upper portion of the tower to effect fractionation of vapors therewithin, collecting resulting condensate at a point substantially below the point I at which said vapors are introduced, vaporizing a portion of said collected condensate, separately withdrawing from the tower an overhead vapor fraction and unvaporized portions of said collected condensate, and withdrawing an intermediate cut by taking off vapors from a section of the tower intermediate the point at "which vapors are introduced and the *point of collection of condensate; v V 6; The method of fractionating hydrocarbon oil vapors which comprises introducing hydrocarbon 'oil vapors into a fractionating tower at an intermediat'epoint thereof, cooling the upper portion ofthe tower toeffect fractionation of densate at a point substantially below the point at whichsaid vapors' are introducedph'eating said collected condensate to effect vaporization of ;-a*-p"ortion' thereof, separately withdrawing from the" tower an overhead vapor fraction and unvaporized portions of said collected condensate, and withdrawing an intermediate cut by taking off vapors from a section of the tower intermediate the point at which vapors are introduced and the point'of collection of condensate.

7. Apparatus for the fractionation of hydrocarbon oil vapors comprising, a fractionating tower, means for supplying hydrocarbonoil vavaporstherewithin,= collecting resulting conpors to said tower at an intermediate point I thereof, means for cooling the upper portion of the tower to effect fractionation of vapors therewithin, means for effecting vaporizationof a portion of condensate formed within said tower,

said vaporizing means being positioned substantially below the point at which vapors are introduced into the tower, means for withdrawing 8. Apparatus for the fractionation of hydro-- vapors from said tower at a point intermediate carbon oil vapors comprising, a fractionating;

tower, means for supplying hydrocarbon oil vapors to said tower at an intermediate point thereof, means for cooling the upper portion of the tower to effect fractionation-of the vapors therewithin, means for collecting resulting condensate within said tower at a point substantially below the point at which vapors are introduced thereinto, means for vaporizing a portion of said collected condensate, means for withdrawing vapors from the tower at a point intermediate the point at which vapors are introduced thereinto and the point at which'condensate is collected, means for withdrawing thereof, means for cooling the upper portion of the tower to effect fractionation of vapors therewithin, means for collecting resulting condensate within said tower at a point substantially below the point at which vapors are introduced thereinto, means for heating and thereby vaporizing a portion of said collected condensate, means for withdrawing vapors'from the tower at a point intermediate the point at which vapors are introduced thereinto and the pointat which condensate is collected, means for withdrawing overhead vapors from the tower, and means for withdrawing from the tower unvaporized portions of said collected condensate.

. 10. The method of fractionatingand separating mixed vapors of hydrocarbon oil containing constituents boiling within the range of temperature suitable for a kerosene, fraction, together with constituents boiling at temperatures both higher and lower than said kerosene temperature range, which comprisesintroducing the mixed vapors'intoa fractionating tower at an intermediate point thereof, cooling the upper portion of the tower to efiect' fractionation of vapors therewithin,.subjecting resulting condensate to vaporization at a point within said tower below the point at which said vapors are in-' troduced, separately withdrawing from the tower an overhead vapor fraction and 'unvaporized portions of said condensate, separately with-,

drawing an intermediate fraction by taking off vapors froma section ofthe tower intermediate the point at which vapors are introduced and the point at whichsaid condensate is-subjected' to vaporization,and-controlling the temperatures of the upper and lower portions-of the; 

